Dual pump VFD controlled system for electric fracturing operations

ABSTRACT

The present invention provides a method and system for providing on-site electrical power to a fracturing operation, and an electrically powered fracturing system. Natural gas can be used to drive a turbine generator in the production of electrical power. A scalable, electrically powered fracturing fleet is provided to pump fluids for the fracturing operation, obviating the need for a constant supply of diesel fuel to the site and reducing the site footprint and infrastructure required for the fracturing operation, when compared with conventional systems.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Nonprovisional patentapplication Ser. No. 15/086,829 filed Mar. 31, 2016 which is acontinuation of U.S. Nonprovisional patent application Ser. No.13/441,334 filed Apr. 6, 2012 and granted as U.S. Pat. No. 9,366,114 onJun. 14, 2016 which claims the benefit, and priority benefit, of U.S.Provisional Patent Application Ser. No. 61/472,861 filed Apr. 7, 2011,titled “MOBILE, MODULAR, ELECTRICALLY POWERED SYSTEM FOR USE INFRACTURING UNDERGROUND FORMATIONS,” the disclosure of which isincorporated herein in its entirety.

BACKGROUND Field of Invention

This invention relates generally to hydraulic stimulation of undergroundhydrocarbon-bearing formations, and more particularly, to the generationand use of electrical power to deliver fracturing fluid to a wellbore.

Description of the Related Art

Over the life cycle of a typical hydrocarbon-producing wellbore, variousfluids (along with additives, proppants, gels, cement, etc. . . . ) canbe delivered to the wellbore under pressure and injected into thewellbore. Surface pumping systems must be able to accommodate thesevarious fluids. Such pumping systems are typically mobilized on skids ortractor-trailers and powered using diesel motors.

Technological advances have greatly improved the ability to identify andrecover unconventional oil and gas resources. Notably, horizontaldrilling and multi-stage fracturing have led to the emergence of newopportunities for natural gas production from shale formations. Forexample, more than twenty fractured intervals have been reported in asingle horizontal wellbore in a tight natural gas formation. However,significant fracturing operations are required to recover theseresources.

Currently contemplated natural gas recovery opportunities requireconsiderable operational infrastructure, including large investments infracturing equipment and related personnel. Notably, standard fluidpumps require large volumes of diesel fuel and extensive equipmentmaintenance programs. Typically, each fluid pump is housed on adedicated truck and trailer configuration. With average fracturingoperations requiring as many as fifty fluid pumps, the on-site area, or“footprint”, required to accommodate these fracturing operations ismassive. As a result, the operational infrastructure required to supportthese fracturing operations is extensive. Greater operationalefficiencies in the recovery of natural gas would be desirable.

When planning large fracturing operations, one major logistical concernis the availability of diesel fuel. The excessive volumes of diesel fuelrequired necessitates constant transportation of diesel tankers to thesite, and results in significant carbon dioxide emissions. Others haveattempted to decrease fuel consumption and emissions by running largepump engines on “Bi-Fuel”, blending natural gas and diesel fueltogether, but with limited success. Further, attempts to decrease thenumber of personnel on-site by implementing remote monitoring andoperational control have not been successful, as personnel are stillrequired on-site to transport the equipment and fuel to and from thelocation.

SUMMARY

Various illustrative embodiments of a system and method for hydraulicstimulation of underground hydrocarbon-bearing formations are providedherein. In accordance with an aspect of the disclosed subject matter, amethod of delivering fracturing fluid to a wellbore is provided. Themethod can comprise the steps of: providing a dedicated source ofelectric power at a site containing a wellbore to be fractured;providing one or more electric fracturing modules at the site, eachelectric fracturing module comprising an electric motor and a coupledfluid pump, each electric motor operatively associated with thededicated source of electric power; providing a wellbore treatment fluidfor pressurized delivery to a wellbore, wherein the wellbore treatmentfluid can be continuous with the fluid pump and with the wellbore; andoperating the fracturing unit using electric power from the dedicatedsource to pump the treatment fluid to the wellbore.

In certain illustrative embodiments, the dedicated source of electricalpower is a turbine generator. A source of natural gas can be provided,whereby the natural gas drives the turbine generator in the productionof electrical power. For example, natural gas can be provided bypipeline, or natural gas produced on-site. Liquid fuels such ascondensate can also be provided to drive the turbine generator.

In certain illustrative embodiments, the electric motor can be an ACpermanent magnet motor and/or a variable speed motor. The electric motorcan be capable of operation in the range of up to 1500 rpms and up to20,000 ft/lbs of torque. The pump can be a triplex or quintiplex plungerstyle fluid pump.

In certain illustrative embodiments, the method can further comprise thesteps of: providing an electric blender module continuous and/oroperatively associated with the fluid pump, the blender modulecomprising: a fluid source, a fluid additive source, and a centrifugalblender tub, and supplying electric power from the dedicated source tothe blender module to effect blending of the fluid with fluid additivesto generate the treatment fluid.

In accordance with another aspect of the disclosed subject matter, asystem for use in delivering pressurized fluid to a wellbore isprovided. The system can comprise: a well site comprising a wellbore anda dedicated source of electricity; an electrically powered fracturingmodule operatively associated with the dedicated source of electricity,the electrically powered fracturing module comprising an electric motorand a fluid pump coupled to the electric motor; a source of treatmentfluid, wherein the treatment fluid can be continuous with the fluid pumpand with the wellbore; and a control system for regulating thefracturing module in delivery of treatment fluid from the treatmentfluid source to the wellbore.

In certain illustrative embodiments, the source of treatment fluid cancomprise an electrically powered blender module operatively associatedwith the dedicated source of electricity. The system can furthercomprise a fracturing trailer at the well site for housing one or morefracturing modules. Each fracturing module can be adapted for removablemounting on the trailer. The system can further comprise a replacementpumping module comprising a pump and an electric motor, the replacementpumping module adapted for removable mounting on the trailer. In certainillustrative embodiments, the replacement pumping module can be anitrogen pumping module, or a carbon dioxide pumping module. Thereplacement pumping module can be, for example, a high torque, low ratemotor or a low torque, high rate motor.

In accordance with another aspect of the disclosed subject matter, afracturing module for use in delivering pressurized fluid to a wellboreis provided. The fracturing module can comprise: an AC permanent magnetmotor capable of operation in the range of up to 1500 rpms and up to20,000 ft/lbs of torque; and a plunger-style fluid pump coupled to themotor.

In accordance with another aspect of the disclosed subject matter, amethod of blending a fracturing fluid for delivery to a wellbore to befractured is provided. A dedicated source of electric power can beprovided at a site containing a wellbore to be fractured. At least oneelectric blender module can be provided at the site. The electricblender module can include a fluid source, a fluid additive source, anda blender tub. Electric power can be supplied from the dedicated sourceto the electric blender module to effect blending of a fluid from thefluid source with a fluid additive from the fluid additive source togenerate the fracturing fluid. The dedicated source of electrical powercan be a turbine generator. A source of natural gas can be provided,wherein the natural gas is used to drive the turbine generator in theproduction of electrical power. The fluid from the fluid source can beblended with the fluid additive from the fluid additive source in theblender tub. The electric blender module can also include at least oneelectric motor that is operatively associated with the dedicated sourceof electric power and that effects blending of the fluid from the fluidsource with the fluid additive from the fluid additive source.

In certain illustrative embodiments, the electric blender module caninclude a first electric motor and a second electric motor, each ofwhich is operatively associated with the dedicated source of electricpower. The first electric motor can effect delivery of the fluid fromthe fluid source to the blending tub. The second electric motor caneffect blending of the fluid from the fluid source with the fluidadditive from the fluid additive source in the blending tub. In certainillustrative embodiments, an optional third electric motor may also bepresent, that can also be operatively associated with the dedicatedsource of electric power. The third electric motor can effect deliveryof the fluid additive from the fluid additive source to the blendingtub.

In certain illustrative embodiments, the electric blender module caninclude a first blender unit and a second blender unit, each disposedadjacent to the other on the blender module and each capable ofindependent operation, or collectively capable of cooperative operation,as desired. The first blender unit and the second blender unit can eachinclude a fluid source, a fluid additive source, and a blender tub. Thefirst blender unit and the second blender unit can each have at leastone electric motor that is operatively associated with the dedicatedsource of electric power and that effects blending of the fluid from thefluid source with the fluid additive from the fluid additive source.Alternatively, the first blender unit and the second blender unit caneach have a first electric motor and a second electric motor, bothoperatively associated with the dedicated source of electric power,wherein the first electric motor effects delivery of the fluid from thefluid source to the blending tub and the second electric motor effectsblending of the fluid from the fluid source with the fluid additive fromthe fluid additive source in the blending tub. In certain illustrativeembodiments, the first blender unit and the second blender unit can eachalso have a third electric motor operatively associated with thededicated source of electric power, wherein the third electric motoreffects delivery of the fluid additive from the fluid additive source tothe blending tub.

In accordance with another aspect of the disclosed subject matter, anelectric blender module for use in delivering a blended fracturing fluidto a wellbore is provided. The electric blender module can include afirst electrically driven blender unit and a first inlet manifoldcoupled to the first electrically driven blender unit and capable ofdelivering an unblended fracturing fluid thereto. A first outletmanifold can be coupled to the first electrically driven blender unitand can be capable of delivering the blended fracturing fluid awaytherefrom. A second electrically driven blender unit can be provided. Asecond inlet manifold can be coupled to the second electrically drivenblender unit and capable of delivering the unblended fracturing fluidthereto. A second outlet manifold can be coupled to the secondelectrically driven blender unit and can be capable of delivering theblended fracturing fluid away therefrom. An inlet crossing line can becoupled to both the first inlet manifold and the second inlet manifoldand can be capable of delivering the unblended fracturing fluidtherebetween. An outlet crossing line can be coupled to both the firstoutlet manifold and the second outlet manifold and can be capable ofdelivering the blended fracturing fluid therebetween. A skid can beprovided for housing the first electrically driven blender unit, thefirst inlet manifold, the second electrically driven blender unit, andthe second inlet manifold.

Other aspects and features of the present invention will become apparentto those of ordinary skill in the art upon review of the followingdetailed description in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the presently disclosed subject matter can beobtained when the following detailed description is considered inconjunction with the following drawings, wherein:

FIG. 1 is a schematic plan view of a traditional fracturing site;

FIG. 2 is a schematic plan view of a fracturing site in accordance withcertain illustrative embodiments described herein;

FIG. 3 is a schematic perspective view of a fracturing trailer inaccordance with certain illustrative embodiments described herein;

FIG. 4A is a schematic perspective view of a fracturing module inaccordance with certain illustrative embodiments described herein;

FIG. 4B is a schematic perspective view of a fracturing module withmaintenance personnel in accordance with certain illustrativeembodiments described herein;

FIG. 5A is a schematic side view of a blender module in accordance withcertain illustrative embodiments described herein;

FIG. 5B is an end view of the blender module shown in FIG. 4A;

FIG. 5C is a schematic top view of a blender module in accordance withcertain illustrative embodiments described herein;

FIG. 5D is a schematic side view of the blender module shown in FIG. 5C;

FIG. 5E is a schematic perspective view of the blender module shown inFIG. 5C;

FIG. 6 is a schematic top view of an inlet manifold for a blender modulein accordance with certain illustrative embodiments described herein;and

FIG. 7 is a schematic top view of an outlet manifold for a blendermodule in accordance with certain illustrative embodiments describedherein.

DETAILED DESCRIPTION

The presently disclosed subject matter generally relates to anelectrically powered fracturing system and a system and method forproviding on-site electrical power and delivering fracturing fluid to awellbore at a fracturing operation.

In a conventional fracturing operation, a “slurry” of fluids andadditives is injected into a hydrocarbon bearing rock formation at awellbore to propagate fracturing. Low pressure fluids are mixed withchemicals, sand, and, if necessary, acid, and then transferred at mediumpressure and high rate to vertical and/or deviated portions of thewellbore via multiple high pressure, plunger style pumps driven bydiesel fueled prime movers. The majority of the fluids injected will beflowed back through the wellbore and recovered, while the sand willremain in the newly created fracture, thus “propping” it open andproviding a permeable membrane for hydrocarbon fluids and gases to flowthrough so they may be recovered.

According to the illustrative embodiments described herein, natural gas(either supplied to the site or produced on-site) can be used to drive adedicated source of electrical power, such as a turbine generator, forhydrocarbon-producing wellbore completions. A scalable, electricallypowered fracturing fleet is provided to deliver pressurized treatmentfluid, such as fracturing fluid, to a wellbore in a fracturingoperation, obviating the need for a constant supply of diesel fuel tothe site and reducing the site footprint and infrastructure required forthe fracturing operation, when compared with conventional operations.The treatment fluid provided for pressurized delivery to the wellborecan be continuous with the wellbore and with one or more components ofthe fracturing fleet, in certain illustrative embodiments. In theseembodiments, continuous generally means that downhole hydrodynamics aredependent upon constant flow (rate and pressure) of the deliveredfluids, and that there should not be any interruption in fluid flowduring delivery to the wellbore if the fracture is to propagate asdesired. However, it should not be interpreted to mean that operationsof the fracturing fleet cannot generally be stopped and started, aswould be understood by one of ordinary skill in the art.

With reference to FIG. 1, a site plan for a traditional fracturingoperation on an onshore site is shown. Multiple trailers 5 are provided,each having at least one diesel tank mounted or otherwise disposedthereon. Each trailer 5 is attached to a truck 6 to permit refueling ofthe diesel tanks as required. Trucks 6 and trailers 5 are located withinregion A on the fracturing site. Each truck 6 requires a dedicatedoperator. One or more prime movers are fueled by the diesel and are usedto power the fracturing operation. One or more separate chemicalhandling skids 7 are provided for housing of blending tanks and relatedequipment.

With reference to FIG. 2, an illustrative embodiment of a site plan foran electrically powered fracturing operation on a onshore site is shown.The fracturing operation includes one or more trailers 10, each housingone or more fracturing modules 20 (see FIG. 3). Trailers 10 are locatedin region B on the fracturing site. One or more natural gas-poweredturbine generators 30 are located in region C on the site, which islocated a remote distance D from region B where the trailers 10 andfracturing modules 20 are located, for safety reasons. Turbinegenerators 30 replace the diesel prime movers utilized in the site planof FIG. 1. Turbine generators 30 provide a dedicated source of electricpower on-site. There is preferably a physical separation between thenatural gas-based power generation in region C and the fracturingoperation and wellbore located in region B. The natural gas-based powergeneration can require greater safety precautions than the fracturingoperation and wellhead. Accordingly, security measures can be taken inregion C to limit access to this more hazardous location, whilemaintaining separate safety standards in region B where the majority ofsite personnel are typically located. Further, the natural gas poweredsupply of electricity can be monitored and regulated remotely such that,if desired, no personnel are required to be within region C duringoperation.

Notably, the setup of FIG. 2 requires significantly less infrastructurethan the setup shown in FIG. 1, while providing comparable pumpingcapacity. Fewer trailers 10 are present in region B of FIG. 2 than thetrucks 6 and trailers 5 in region A of FIG. 1, due to the lack of needfor a constant diesel fuel supply. Further, each trailer 10 in FIG. 2does not need a dedicated truck 6 and operator as in FIG. 1. Fewerchemical handling skids 7 are required in region B of FIG. 2 than inregion A of FIG. 1, as the skids 7 in FIG. 2 can be electricallypowered. Also, by removing diesel prime movers, all associated machinerynecessary for power transfer can be eliminated, such as thetransmission, torque converter, clutch, drive shaft, hydraulic system,etc. . . . , and the need for cooling systems, including circulatingpumps and fluids, is significantly reduced. In an illustrativeembodiment, the physical footprint of the on-site area in region B ofFIG. 2 is about 80% less than the footprint for the conventional systemin region A of FIG. 1.

With reference to the illustrative embodiments of FIG. 3, trailer 10 forhousing one or more fracturing modules 20 is shown. Trailer 10 can alsobe a skid, in certain illustrative embodiments. Each fracturing module20 can include an electric motor 21 and a fluid pump 22 coupled thereto.During fracturing, fracturing module 20 is operatively associated withturbine generator 30 to receive electric power therefrom. In certainillustrative embodiments, a plurality of electric motors 21 and pumps 22can be transported on a single trailer 10. In the illustrativeembodiments of FIG. 3, four electric motors 21 and pumps 22 aretransported on a single trailer 10. Each electric motor 21 is paired toa pump 22 as a single fracturing module 20. Each fracturing module 20can be removably mounted to trailer 10 to facilitate ease of replacementas necessary. Fracturing modules 20 utilize electric power from turbinegenerator 30 to pump the fracturing fluid directly to the wellbore.

Electrical Power Generation

The use of a turbine to directly drive a pump has been previouslyexplored. In such systems, a transmission is used to regulate turbinepower to the pump to allow for speed and torque control. In the presentoperation, natural gas is instead used to drive a dedicated power sourcein the production of electricity. In illustrative embodiments, thededicated power source is an on-site turbine generator. The need for atransmission is eliminated, and generated electricity can be used topower the fracturing modules, blenders, and other on-site operations asnecessary.

Grid power may be accessible on-site in certain fracturing operations,but the use of a dedicated power source is preferred. During startup ofa fracturing operation, massive amounts of power are required such thatthe use of grid power would be impractical. Natural gas poweredgenerators are more suitable for this application based on the likelyavailability of natural gas on-site and the capacity of natural gasgenerators for producing large amounts of power. Notably, the potentialfor very large instantaneous adjustments in power drawn from the gridduring a fracturing operation could jeopardize the stability andreliability of the grid power system. Accordingly, a site-generated anddedicated source of electricity provides a more feasible solution inpowering an electric fracturing system. In addition, a dedicated on-siteoperation can be used to provide power to operate other local equipment,including coiled tubing systems, service rigs, etc. . . . .

In an illustrative embodiment, a single natural gas powered turbinegenerator 30, as housed in a restricted area C of FIG. 2, can generatesufficient power (for example 31 MW at 13,800 volts AC power) to supplyseveral electric motors 21 and pumps 22, avoiding the current need todeliver and operate each fluid pump from a separate diesel-poweredtruck. A turbine suitable for this purpose is a TM2500+ turbinegenerator sold by General Electric. Other generation packages could besupplied by Pratt & Whitney or Kawasaki for example. Multiple optionsare available for turbine power generation, depending on the amount ofelectricity required. In an illustrative embodiment, liquid fuels suchas condensate can also be provided to drive turbine generator 30 insteadof, or in addition to, natural gas. Condensate is less expensive thandiesel fuels, thus reducing operational costs.

Fracturing Module

With reference to FIGS. 4A and 4B, an illustrative embodiment offracturing module 20 is provided. Fracturing module 20 can include anelectric motor 21 coupled to one or more electric pumps 22, in certainillustrative embodiments. A suitable pump is a quintiplex or triplexplunger style pump, for example, the SWGS-2500 Well Service Pump sold byGardner Denver, Inc.

Electric motor 21 is operatively associated with turbine generator 30,in certain embodiments. Typically, each fracturing module 20 will beassociated with a drive housing for controlling electric motor 21 andpumps 22, as well as an electrical transformer and drive unit 50 (seeFIG. 3) to step down the voltage of the power from turbine generator 30to a voltage appropriate for electric motor 21. The electricaltransformer and drive unit 50 can be provided as an independent unit forassociation with fracturing module 20, or can be permanently fixed tothe trailer 10, in various embodiments. If permanently fixed, thentransformer and drive unit 50 can be scalable to allow addition orsubtraction of pumps 22 or other components to accommodate anyoperational requirements.

Each pump 22 and electric motor 21 are modular in nature so as tosimplify removal and replacement from fracturing module 20 formaintenance purposes. Removal of a single fracturing module 20 fromtrailer 10 is also simplified. For example, any fracturing module 20 canbe unplugged and unpinned from trailer 10 and removed, and anotherfracturing module 20 can be installed in its place in a matter ofminutes.

In the illustrative embodiment of FIG. 3, trailer 10 can house fourfracturing modules 20, along with a transformer and drive unit 50. Inthis particular configuration, each single trailer 10 provides morepumping capacity than four of the traditional diesel powered fracturingtrailers 5 of FIG. 1, as parasitic losses are minimal in the electricfracturing system compared to the parasitic losses typical of dieselfueled systems. For example, a conventional diesel powered fluid pump israted for 2250 hp. However, due to parasitic losses in the transmission,torque converter and cooling systems, diesel fueled systems typicallyonly provide 1800 hp to the pumps. In contrast, the present system candeliver a true 2500 hp directly to each pump 22 because pump 22 isdirectly coupled to electric motor 21. Further, the nominal weight of aconventional fluid pump is up to 120,000 lbs. In the present operation,each fracturing module 20 weighs approximately 28,000 lbs., thusallowing for placement of four pumps 22 in the same physical dimension(size and weight) as the spacing needed for a single pump inconventional diesel systems, as well as allowing for up to 10,000 hptotal to the pumps. In other embodiments, more or fewer fracturingmodules 20 may be located on trailer 10 as desired or required foroperational purposes.

In certain illustrative embodiments, fracturing module 20 can include aelectric motor 21 that is an AC permanent magnet motor capable ofoperation in the range of up to 1500 rpms and up to 20,000 ft/lbs oftorque. Fracturing module 20 can also include a pump 22 that is aplunger-style fluid pump coupled to electric motor 21. In certainillustrative embodiments, fracturing module 20 can have dimensions ofapproximately 136″ width×108″ length×100″ height. These dimensions wouldallow fracturing module 20 to be easily portable and fit with a ISOintermodal container for shipping purposes without the need fordisassembly. Standard sized ISO container lengths are typically 20′, 40′or 53′. In certain illustrative embodiments, fracturing module 20 canhave dimensions of no greater than 136″ width×108″ length×100″ height.These dimensions for fracturing module 20 would also allow crew membersto easily fit within the confines of fracturing module 20 to makerepairs, as illustrated in FIG. 4b . In certain illustrativeembodiments, fracturing module 20 can have a width of no greater than102″ to fall within shipping configurations and road restrictions. In aspecific embodiment, fracturing module 20 is capable of operating at2500 hp while still having the above specified dimensions and meetingthe above mentioned specifications for rpms and ft/lbs of torque.

Electric Motor

With reference to the illustrative embodiments of FIGS. 2 and 3, amedium low voltage AC permanent magnet electric motor 21 receiveselectric power from turbine generator 30, and is coupled directly topump 22. In order to ensure suitability for use in fracturing, electricmotor 21 should be capable of operation up to 1,500 rpm with a torque ofup to 20,000 ft/lbs, in certain illustrative embodiments. A motorsuitable for this purpose is sold under the trademark TeraTorq® and isavailable from Comprehensive Power, Inc. of Marlborough, Mass. A compactmotor of sufficient torque will allow the number of fracturing modules20 placed on each trailer 10 to be maximized.

Blender

For greater efficiency, conventional diesel powered blenders andchemical addition units can be replaced with electrically poweredblender units. In certain illustrative embodiments as described herein,the electrically powered blender units can be modular in nature forhousing on trailer 10 in place of fracturing module 20, or housedindependently for association with each trailer 10. An electric blendingoperation permits greater accuracy and control of fracturing fluidadditives. Further, the centrifugal blender tubs typically used withblending trailers to blend fluids with proppant, sand, chemicals, acid,etc. . . . prior to delivery to the wellbore are a common source ofmaintenance costs in traditional fracturing operations.

With reference to FIGS. 5A-5E and FIGS. 6-7, illustrative embodiments ofa blender module 40 and components thereof are provided. Blender module40 can be operatively associated with turbine generator 30 and capableof providing fractioning fluid to pump 22 for delivery to the wellbore.In certain embodiments, blender module 40 can include at least one fluidadditive source 44, at least one fluid source 48, and at least onecentrifugal blender tub 46. Electric power can be supplied from turbinegenerator 30 to blender module 40 to effect blending of a fluid fromfluid source 48 with a fluid additive from fluid additive source 44 togenerate the fracturing fluid. In certain embodiments, the fluid fromfluid source 48 can be, for example, water, oils or methanol blends, andthe fluid additive from fluid additive source 44 can be, for example,friction reducers, gellents, gellent breakers or biocides.

In certain illustrative embodiments, blender module 40 can have a dualconfiguration, with a first blender unit 47 a and a second blender unit47 b positioned adjacent to each other. This dual configuration isdesigned to provide redundancy and to facilitate access for maintenanceand replacement of components as needed. In certain embodiments, eachblender unit 47 a and 47 b can have its own electrically-powered suctionand tub motors disposed thereon, and optionally, otherelectrically-powered motors can be utilized for chemical additionaland/or other ancillary operational functions, as discussed furtherherein.

For example, in certain illustrative embodiments, first blender unit 47a can have a plurality of electric motors including a first electricmotor 43 a and a second electric motor 41 a that are used to drivevarious components of blender module 40. Electric motors 41 a and 43 acan be powered by turbine generator 30. Fluid can be pumped into blendermodule 40 through an inlet manifold 48 a by first electric motor 43 aand added to tub 46 a. Thus, first electric motor 43 a acts as a suctionmotor. Second electric motor 41 a can drive the centrifugal blendingprocess in tub 46 a. Second electric motor 41 a can also drive thedelivery of blended fluid out of blender module 40 and to the wellborevia an outlet manifold 49 a. Thus, second electric motor 41 a acts as atub motor and a discharge motor. In certain illustrative embodiments, athird electric motor 42 a can also be provided. Third electric motor 42a can also be powered by turbine generator 30, and can power delivery offluid additives to blender 46 a. For example, proppant from a hopper 44a can be delivered to a blender tub 46 a, for example, a centrifugalblender tub, by an auger 45 a, which is powered by third electric motor42 a.

Similarly, in certain illustrative embodiments, second blender unit 47 bcan have a plurality of electric motors including a first electric motor43 b and a second electric motor 41 b that are used to drive variouscomponents of blender module 40. Electric motors 41 b and 43 b can bepowered by turbine generator 30. Fluid can be pumped into blender module40 through an inlet manifold 48 b by first electric motor 43 b and addedto tub 46 b. Thus, second electric motor 43 a acts as a suction motor.Second electric motor 41 b can drive the centrifugal blending process intub 46 b. Second electric motor 41 b can also drive the delivery ofblended fluid out of blender module 40 and to the wellbore via an outletmanifold 49 b. Thus, second electric motor 41 b acts as a tub motor anda discharge motor. In certain illustrative embodiments, a third electricmotor 42 b can also be provided. Third electric motor 42 b can also bepowered by turbine generator 30, and can power delivery of fluidadditives to blender 46 b. For example, proppant from a hopper 44 b canbe delivered to a blender tub 46 b, for example, a centrifugal blendertub, by an auger 45 b, which is powered by third electric motor 42 b.

Blender module 40 can also include a control cabin 53 for housingequipment controls for first blender unit 47 a and second blender unit47 b, and can further include appropriate drives and coolers asrequired.

Conventional blenders powered by a diesel hydraulic system are typicallyhoused on a forty-five foot tractor trailer and are capable ofapproximately 100 bbl/min. In contrast, the dual configuration ofblender module 40 having first blender unit 47 a and second blender unit47 b can provide a total output capability of 240 bbl/min in the samephysical footprint as a conventional blender, without the need for aseparate backup unit in case of failure.

Redundant system blenders have been tried in the past with limitedsuccess, mostly due to problems with balancing weights of the trailerswhile still delivering the appropriate amount of power. Typically, twoseparate engines, each approximately 650 hp, have been mounted side byside on the nose of the trailer. In order to run all of the necessarysystems, each engine must drive a mixing tub via a transmission, dropbox and extended drive shaft. A large hydraulic system is also fitted toeach engine to run all auxiliary systems such as chemical additions andsuction pumps. Parasitic power losses are very large and the hosing andwiring is complex.

In contrast, the electric powered blender module 40 described in certainillustrative embodiments herein can relieve the parasitic power lossesof conventional systems by direct driving each piece of criticalequipment with a dedicated electric motor. Further, the electric poweredblender module 40 described in certain illustrative embodiments hereinallows for plumbing routes that are unavailable in conventionalapplications. For example, in certain illustrative embodiments, thefluid source can be an inlet manifold 48 that can have one or more inletcrossing lines 50 (see FIG. 7) that connect the section of inletmanifold 48 dedicated to delivering fluid to first blender unit 47 awith the section of inlet manifold 48 dedicated to delivering fluid tosecond blender unit 47 b. Similarly, in certain illustrativeembodiments, outlet manifold 49 can have one or more outlet crossinglines 51 (see FIG. 6) that connect the section of outlet manifold 49dedicated to delivering fluid from first blender unit 47 a with thesection of outlet manifold 49 dedicated to delivering fluid from secondblender unit 47 b. Crossing lines 50 and 51 allow flow to be routed ordiverted between first blender unit 47 a and second blender unit 47 b.Thus, blender module 40 can mix from either side, or both sides, and/ordischarge to either side, or both sides, if necessary. As a result, theattainable rates for the electric powered blender module 40 are muchlarger that of a conventional blender. In certain illustrativeembodiments, each side (i.e., first blender unit 47 a and second blenderunit 47 b) of blender module 40 is capable of approximately 120 bbl/min.Also, each side (i.e., first blender unit 47 a and second blender unit47 b) can move approximately 15 t/min of sand, at least in part becausethe length of auger 45 is shorter (approximately 6′) as compared toconventional units (approximately 12′).

In certain illustrative embodiments, blender module 40 can be scaleddown or “downsized” to a single, compact module comparable in size anddimensions to fracturing module 20 described herein. For smallerfracturing or treatment jobs requiring fewer than four fracturingmodules 20, a downsized blender module 40 can replace one of thefracturing modules 20 on trailer 10, thus reducing operational costs andimproving transportability of the system.

Control System

A control system can be provided for regulating various equipment andsystems within the electric powered fractioning operation. For example,in certain illustrative embodiments, the control system can regulatefracturing module 20 in delivery of treatment fluid from blender module30 to pumps 22 for delivery to the wellbore. Controls for theelectric-powered operation described herein are a significantimprovement over that of conventional diesel powered systems. Becauseelectric motors are controlled by variable frequency drives, absolutecontrol of all equipment on location can be maintained from one centralpoint. When the system operator sets a maximum pressure for thetreatment, the control software and variable frequency drives calculatea maximum current available to the motors. Variable frequency drivesessentially “tell” the motors what they are allowed to do.

Electric motors controlled via variable frequency drive are far saferand easier to control than conventional diesel powered equipment. Forexample, conventional fleets with diesel powered pumps utilize anelectronically controlled transmission and engine on the unit. There canbe up to fourteen different parameters that need to be monitored andcontrolled for proper operation. These signals are typically sent viahardwired cable to an operator console controlled by the pump driver.The signals are converted from digital to analog so the inputs can bemade via switches and control knobs. The inputs are then converted fromanalog back to digital and sent back to the unit. The control module onthe unit then tells the engine or transmission to perform the requiredtask and the signal is converted to a mechanical operation. This processtakes time.

Accidental over-pressures are quite common in these conventionaloperations, as the signal must travel to the console, back to the unitand then perform a mechanical function. Over-pressures can occur inmilliseconds due to the nature of the operations. These are usually dueto human error, and can be as simple as a single operator failing toreact to a command. They are often due to a valve being closed, whichaccidentally creates a “deadhead” situation.

For example, in January of 2011, a large scale fractioning operation wastaking place in the Horn River Basin of north-eastern British Columbia,Canada. A leak occurred in one of the lines and a shutdown order wasgiven. The master valve on the wellhead was then closed remotely.Unfortunately, multiple pumps were still rolling and a systemover-pressure ensued. Treating iron rated for 10,000 psi was taken towell over 15,000 psi. A line attached to the well also separated,causing it to whip around. The incident caused a shutdown interruptionto the entire operation for over a week while investigation and damageassessment were performed.

The control system provided according to the present illustrativeembodiments, being electrically powered, virtually eliminates thesetypes of scenarios from occurring. A maximum pressure value set at thebeginning of the operation is the maximum amount of power that can besent to electric motor 21 for pump 22. By extrapolating a maximumcurrent value from this input, electric motor 21 does not have theavailable power to exceed its operating pressure. Also, because thereare virtually no mechanical systems between pump 22 and electric motor21, there is far less “moment of inertia” of gears and clutches to dealwith. A near instantaneous stop of electric motor 21 results in a nearinstantaneous stop of pump 22.

An electrically powered and controlled system as described hereingreatly increases the ease in which all equipment can be synced orslaved to each other. This means a change at one single point will becarried out by all pieces of equipment, unlike with diesel equipment.For example, in conventional diesel powered operations, the blendertypically supplies all the necessary fluids to the entire system. Inorder to perform a rate change to the operation, the blender must changerate prior to the pumps changing rates. This can often result inaccidental overflow of the blender tubs and/or cavitation of the pumpsdue to the time lag of each piece of equipment being given manualcommands.

In contrast, the present operation utilizes a single point control thatis not linked solely to blender operations, in certain illustrativeembodiments. All operation parameters can be input prior to beginningthe fractioning. If a rate change is required, the system will increasethe rate of the entire system with a single command. This means that ifpumps 22 are told to increase rate, then blender module 40 along withthe chemical units and even ancillary equipment like sand belts willincrease rates to compensate automatically.

Suitable controls and computer monitoring for the entire fracturingoperation can take place at a single central location, which facilitatesadherence to pre-set safety parameters. For example, a control center 40is indicated in FIG. 2 from which operations can be managed viacommunications link 41. Examples of operations that can be controlledand monitored remotely from control center 40 via communications link 41can be the power generation function in Area B, or the delivery oftreatment fluid from blender module 40 to pumps 22 for delivery to thewellbore.

Comparison Example

Table 1, shown below, compares and contrasts the operational costs andmanpower requirements for a conventional diesel powered operation (suchas shown in FIG. 1) with those of an electric powered operation (such asshown in FIG. 2).

TABLE 1 Comparison of Conventional Diesel Powered Operation vs. ElectricPowered Operation Diesel Powered Operation Electric Powered OperationTotal fuel cost (diesel) - Total fuel cost (natural gas) - about $80,000per day about $2,300 per day Service interval for diesel engines -Service interval for electric motor - about every 200-300 hours aboutevery 50,000 hours Dedicated crew size - Dedicated crew size - about 40people about 10 people

In Table 1, the “Diesel Powered Operation” utilizes at least 24 pumpsand 2 blenders, and requires at least 54,000 hp to execute thefracturing program on that location. Each pump burns approximately300-400 liters per hour of operation, and the blender units burn acomparable amount of diesel fuel. Because of the fuel consumption andfuel capacity of this conventional unit, it requires refueling duringoperation, which is extremely dangerous and presents a fire hazard.Further, each piece of conventional equipment needs a dedicated tractorto move it and a driver/operator to run it. The crew size required tooperate and maintain a conventional operation such as the one in FIG. 1represents a direct cost for the site operator.

In contrast, the electric powered operation as described herein utilizesa turbine that only consumes about 6 mm scf of natural gas per 24 hours.At current market rates (approximately $2.50 per mmbtu), this equates toa reduction in direct cost to the site operator of over $77,000 per daycompared to the diesel powered operation. Also, the service interval onelectric motors is about 50,000 hours, which allows the majority ofreliability and maintainability costs to disappear. Further, the needfor multiple drivers/operators is reduced significantly, and electricpowered operation means that a single operator can run the entire systemfrom a central location. Crew size can be reduced by around 75%, as onlyabout 10 people are needed on the same location to accomplish the sametasks as conventional operations, with the 10 people including off-sitepersonnel maintenance personnel. Further, crew size does not change withthe amount of equipment used. Thus, the electric powered operation issignificantly more economical.

Modular Design and Alternate Embodiments

As discussed above, the modular nature of the electric poweredfracturing operation described herein provides significant operationaladvantages and efficiencies over traditional fracturing systems. Eachfracturing module 20 sits on trailer 10 which houses the necessarymounts and manifold systems for low pressure suctions and high pressuredischarges. Each fracturing module 20 can be removed from service andreplaced without shutting down or compromising the fractioning spread.For instance, pump 22 can be isolated from trailer 10, removed andreplaced by a new pump 22 in just a few minutes. If fracturing module 20requires service, it can be isolated from the fluid lines, unplugged,un-pinned and removed by a forklift. Another fracturing module 20 can bethen re-inserted in the same fashion, realizing a drastic time savings.In addition, the removed fracturing module 20 can be repaired orserviced in the field. In contrast, if one of the pumps in aconventional diesel powered system goes down or requires service, thetractor/trailer combination needs to be disconnected from the manifoldsystem and driven out of the location. A replacement unit must then bebacked into the line and reconnected. Maneuvering these units in thesetight confines is difficult and dangerous.

The presently described electric powered fracturing operation can beeasily adapted to accommodate additional types of pumping capabilitiesas needed. For example, a replacement pumping module can be providedthat is adapted for removable mounting on trailer 10. Replacementpumping module can be utilized for pumping liquid nitrogen, carbondioxide, or other chemicals or fluids as needed, to increase theversatility of the system and broaden operational range and capacity. Ina conventional system, if a nitrogen pump is required, a separate unittruck/trailer unit must be brought to the site and tied into thefractioning spread. In contrast, the presently described operationallows for a replacement nitrogen module with generally the samedimensions as fractioning module 20, so that the replacement module canfit into the same slot on the trailer as fractioning module 20 would.Trailer 10 can contain all the necessary electrical power distributionsas required for a nitrogen pump module so no modifications are required.The same concept would apply to carbon dioxide pump modules or any otherpieces of equipment that would be required. Instead of anothertruck/trailer, a specialized replacement module can instead be utilized.

Natural gas is considered to be the cleanest, most efficient fuel sourceavailable. By designing and constructing “fit for purpose equipment”that is powered by natural gas, it is expected that the fracturingfootprint, manpower, and maintenance requirements can each be reduced byover 60% when compared with traditional diesel-powered operations.

In addition, the presently described electric powered fracturingoperation resolves or mitigates environmental impacts of traditionaldiesel-powered operations. For example, the presently described naturalgas powered operation can provide a significant reduction in carbondioxide emissions as compared to diesel-powered operations. In anillustrative embodiment, a fractioning site utilizing the presentlydescribed natural gas powered operation would have a carbon dioxideemissions level of about 2200 kg/hr, depending upon the quality of thefuel gas, which represents an approximately 200% reduction from carbondioxide emissions of diesel-powered operations. Also, in an illustrativeembodiment, the presently described natural gas powered operation wouldproduces no greater than about 80 decibels of sound with a silencerpackage utilized on turbine 30, which meets OSHA requirements for noiseemissions. By comparison, a conventional diesel-powered fractioning pumprunning at full rpm emits about 105 decibels of sound. When multiplediesel-powered fractioning pumps are running simultaneously, noise is asignificant hazard associated with conventional operations.

In certain illustrative embodiments, the electric-powered fractioningoperation described herein can also be utilized for offshore oil and gasapplications, for example, fracturing of a wellbore at an offshore site.Conventional offshore operations already possess the capacity togenerate electric power on-site. These vessels are typically diesel overelectric, which means that the diesel powerplant on the vessel generateselectricity to meet all power requirements including propulsion.Conversion of offshore pumping services to run from an electrical powersupply will allow transported diesel fuel to be used in power generationrather than to drive the fracturing operation, thus reducing diesel fuelconsumption. The electric power generated from the offshore vessel'spower plant (which is not needed during station keeping) can be utilizedto power one or more fracturing modules 10. This is far cleaner, saferand more efficient than using diesel powered equipment. Fracturingmodules 10 are also smaller and lighter than the equipment typicallyused on the deck of offshore vessels, thus removing some of the currentballast issues and allowing more equipment or raw materials to betransported by the offshore vessels.

In a deck layout for a conventional offshore stimulation vessel, skidbased, diesel powered pumping equipment and storage facilities on thedeck of the vessel create ballast issues. Too much heavy equipment onthe deck of the vessel causes the vessel to have higher center ofgravity. Also, fuel lines must be run to each piece of equipment greatlyincreasing the risk of fuel spills. In illustrative embodiments of adeck layout for an offshore vessel utilizing electric-poweredfractioning operations as described herein, the physical footprint ofthe equipment layout is reduced significantly when compared to theconventional layout. More free space is available on deck, and theweight of equipment is dramatically decreased, thus eliminating most ofthe ballast issues. A vessel already designed as diesel-electric can beutilized. When the vessel is on station at a platform and in stationkeeping mode, the vast majority of the power that the ship's engines aregenerating can be run up to the deck to power modules. The storagefacilities on the vessel can be placed below deck, further lowering thecenter of gravity, while additional equipment, for instance, a 3-phaseseparator, or coiled tubing unit, can be provided on deck, which isdifficult in existing diesel-powered vessels. These benefits, coupledwith the electronic control system, give a far greater advantage overconventional vessels.

While the present description has specifically contemplated a fracturingsystem, the system can be used to power pumps for other purposes, or topower other oilfield equipment. For example, high rate and pressurepumping equipment, hydraulic fracturing equipment, well stimulationpumping equipment and/or well servicing equipment could also be poweredusing the present system. In addition, the system can be adapted for usein other art fields requiring high torque or high rate pumpingoperations, such as pipeline cleaning or dewatering mines.

It is to be understood that the subject matter herein is not limited tothe exact details of construction, operation, exact materials, orillustrative embodiments shown and described, as modifications andequivalents will be apparent to one skilled in the art. Accordingly, thesubject matter is therefore to be limited only by the scope of theappended claims.

What is claimed is:
 1. A system for use in delivering pressurized fluidto a wellbore to be fractured, comprising: a transportable turbinegenerator; an electric motor electrically connected to the turbinegenerator; a first fracturing fluid pump coupled to the electric motorand configured to be driven by the electric motor and to pump afracturing fluid; a second fracturing fluid pump coupled to the electricmotor and configured to be driven by the electric motor and to pump thefracturing fluid, wherein the second fracturing fluid pump and the firstfracturing fluid pump can operate simultaneously; an electric blendersystem configured to provide the fracturing fluid to the firstfracturing fluid pump and the second fracturing fluid pump, wherein theelectric blender system is electrically connected to the turbinegenerator, and wherein the electric blender system comprises a firstinlet electric motor, a second inlet electric motor, a first electricdischarge motor, and a second electric discharge motor; and a variablefrequency drive electrically coupled to the electric motor, wherein thevariable frequency drive is configured to control a speed of theelectric motor.
 2. The system of claim 1, wherein the variable frequencydrive is configured to control a maximum current available to theelectric motor.
 3. The system of claim 1, wherein the variable frequencydrive is configured to be electrically coupled to the turbine generatorand to provide electric power to the electric motor when the turbinegenerator is disposed at a remote location relative to the electricmotor.
 4. The system of claim 1, wherein the electric motor is avariable speed motor.
 5. The system of claim 1, wherein the turbinegenerator is powered by natural gas.
 6. The system of claim 1, whereinthe turbine generator is powered by condensate liquid fuel.
 7. Thesystem of claim 1, wherein the electric motor and the first fracturingfluid pump are located on a transportable trailer.
 8. The system ofclaim 1, wherein the electric motor, the first fracturing fluid pump,the second fracturing fluid pump and the variable frequency drive arelocated on a transportable trailer.
 9. A system for use in deliveringpressurized fluid to a wellbore to be fractured, comprising: atransportable natural gas-powered dedicated source of generatingelectricity; an electrical motor electrically connected to the dedicatedsource of generating electricity; a first fracturing fluid pump coupledto the electric motor and configured to be driven by the electric motorand to pump a fracturing fluid; a second fracturing fluid pump coupledto the electric motor and configured to be driven by the electric motorand to pump the fracturing fluid, wherein the second fracturing pump andthe first fracturing fluid pump can operate simultaneously; an electricblender system configured to provide the fracturing fluid to the firstfracturing fluid pump and the second fracturing fluid pump, wherein theelectric blender system is electrically connected to the dedicatedsource of generating electricity, and wherein the electric blendersystem comprises a first inlet electric motor, a second inlet electricmotor, a first electric discharge motor, and a second electric dischargemotor; and a variable frequency drive electrically coupled to theelectric motor, wherein the variable frequency drive is configured tocontrol a speed of the electric motor and a maximum current available tothe electric motor.
 10. The system of claim 9, wherein the variablefrequency drive is configured to be electrically coupled to the naturalgas-powered dedicated source and to provide electric power to theelectric motor when the natural gas-powered dedicated source is disposedat a remote location relative to the electric motor.
 11. The system ofclaim 9, wherein the electric motor is a variable speed motor.
 12. Thesystem of claim 9, wherein the electric motor is capable of operating at1500 rpms and 20,000 ft/lbs of torque during fracturing operations. 13.The system of claim 9, wherein the electric motor, the first fracturingfluid pump, the second fracturing fluid pump and the variable frequencydrive are located on a transportable trailer.
 14. A method of deliveringpressurized fluid to a wellbore to be fractured, comprising: providing atransportable turbine generator; providing an electric motor that iselectrically connected to the turbine generator; providing a firstfracturing fluid pump coupled to the electric motor and configured to bedriven by the electric motor and pump a fracturing fluid into a conduitin communication with the wellbore; providing a second fracturing fluidpump coupled to the electric motor and configured to be driven by theelectric motor and pump the fracturing fluid into a conduit incommunication with the wellbore, wherein the second fracturing fluidpump and the first fracturing fluid pump can operate simultaneously;providing an electric blender system configured to provide thefracturing fluid to the first fracturing fluid pump and the secondfracturing fluid pump, wherein the electric blender system iselectrically connected to the turbine generator, and wherein theelectric blender system comprises a first inlet electric motor, a secondinlet electric motor, a first electric discharge motor, and a secondelectric discharge motor; and providing a variable frequency driveelectrically coupled to the electric motor, wherein the variablefrequency drive is configured to control a speed of the electric motor.15. The method of claim 14, wherein the variable frequency drive isconfigured to control a maximum current available to the electric motor.16. The method of claim 14, wherein the variable frequency drive isconfigured to be electrically coupled to the turbine generator and toprovide electric power to the electric motor when the turbine generatoris disposed at a remote location relative to the electric motor.
 17. Themethod of claim 14, wherein the turbine generator is powered by naturalgas.
 18. The method of claim 14, wherein the turbine generator ispowered by condensate liquid fuel.
 19. The method of claim 14, whereinthe electric motor and the first fracturing fluid pump are located on atransportable trailer.
 20. The method of claim 14, wherein the electricmotor, the first fracturing fluid pump, the second fracturing fluid pumpand the variable frequency drive are located on a transportable trailer.